A see-through display merges a display image and an external image, presenting both images in the same physical space. Such a display may be used in a wearable, head-mounted display system; it may be coupled in goggles, a helmet, or other eyewear. The see-through display enables the viewer to view images from a computer, video game, media player, or other electronic device, with privacy and mobility. When configured to present two different display images, one for each eye, this approach may be used for stereoscopic (e.g., virtual-reality) display.
To provide a positive viewing experience, a head-mounted display system may be configured in view of certain ocular relationships. One such relationship is the placement of the focal plane of the display image relative to a background subject in the external scene. If the focal plane of the display image is too far from the background subject, the viewer may have difficulty focusing and may experience eyestrain.